Device for the injection of gases into molten metals and minerals

ABSTRACT

A device for injecting gas into a hot melt, particularly molten metal, is suitable for being installed in the wall, particularly the bottom wall, of the container holding the melt. The device has three main sections including 
     a front section of refractory material which is resistant to the melt in question, and which has a number of perforations (10) for introduction of gas into the melt, 
     a middle section which at least partly consists of heat conductive material and possesses a number of perforations communicating with the perforations of the front section, and 
     a rear section at least the outer (peripheral) part of which is of heat conducting material, which rear section in or close to its peripheral part has a helical duct communicating with the perforations of the middle section and adapted to pass the gas from an external gas source. 
     The middle section is preferably divided into two part sections of which at least one, preferably the foremost part section, is made of a material of high heat conductivity, preferably copper or a copper alloy, whereas the rear part section preferably is of steel.

BACKGROUND OF THE INVENTION

The present invention relates to a device for injecting gases intomolten metal, alloys, minerals and the like, e.g. steel, aluminum,silicon, silicon alloys, to thereby honogenize, refine or in other waystreat the molten material.

The treatment of melts, particularly metal melts, with gases is wellknown within industry, and may have several different aims, e.g.stripping of undesirable, completely or partly dissolved gases from themelt, oxidation or reduction of some of the components of the melt tocompletely or partly eliminate these, e.g. as slag-forming oxides orvolatile oxides; or gaseous reactants which are blown into the melt areintended to react with components thereof forming new, desiredcomponents of the melt. Many different, and partly specific, aims of gastreatment of metal melts are disclosed in the litterature. Examples areshown in Swedish Patent Publications Nos. 375 122; 395 912 and 413 327;and French Pat. Nos. 2 013 546 and 2 012 305.

Several of the well known devices for the above mentioned purposecomprise a porous, refractory body which is permeable to the gas to beinjected or blown in, but not permeable to the molten material which isto be gas treated, whereby the porous body prevents draining of themelt.

One of the drawbacks of porous bodies is that they possess relativelyhigh resistance to penetration of gas and thus relatively low capacityin this respect.

When relatively great amounts of gas are to be injected, injectingdevices are suitably used by which the gas is injected via one orseveral tubes or borings in the device. The above mentioned problem ofpreventing the molten material from penetrating into the injectiondevice must also in this case be solved. If not, there will be a risk ofgreat drawbacks and frequent replacements of the injection device. Aconventional solution of said problem is to circulate cooling fluidthrough part of the injection device whereby melt penetrating into thedevice from the container solidifies and prevents the outflow of themelt. Such an injection device is disclosed by DE-PS No. 2 503 672. Withrespect to embodiments of constructions of injection devices referenceis further, more generally, made to e.g. DE-PS Nos. 1 508 263B and 1 508282B and SE-PS No. 301 733B.

SUMMARY OF THE INVENTION

During the work of development of the injection device according to theinvention the aim has been to provide an improved device for injectinggases into molten metals, alloys etc. (in the following for the sake ofbrevity called "the melt") contained in any container, reactor, ladle orthe like, and where the device is mounted in the wall lining of thecontainer beneath the bath level or preferably in its bottom lining.

Among the requirements to be met by the device the following arementioned more particularly:

(a) High degree of safety against the melt flowing out via the injectiondevice.

(b) Effective dispersion of injected gas in the melt.

(c) High degree of capacity flexibility.

(d) Long working life of the injection device.

(e) Possibility of convenient and quick replacement of the injectiondevice from outside.

(f) Flexible adaptability to different containers/ladles/reactors andthickness of linings.

The injection device of the invention, which has been found to fulfilthese requirements in a very satisfying way, comprises three mainsections.

(1) a front section of refractory material which is also resistant tothe melt in question and which has a number of perforations forsupplying gas to the melt,

(2) a middle section which at least partly consists of heat conductingmaterial and has a number of perforations communicating with theperforations of the front section,

(3) a rear section wherein at least the outer (peripheral) part is madeof heat conducting material, which rear section in or adjacent to itsperipheral parts has a helical duct communicating with perforations ofthe middle section and being provided to convey said gas from anexternal gas source.

According to a preferred embodiment of the invention the front sectionis divided into two part sections of which at least the foremost partsection is made of refractory material, and wherein the perforations ofthe foremost part section are communicating with the perforations of theother (rear) part section through a cavity.

Another preferred embodiment provides that the middle section is dividedinto two part sections, of which at least one, preferably the foremostpart section, is made of a material of high thermal conductivity. Theforemost part section of the middle section preferably comprises copperor a copper alloy. The rear part section of the middle sectionpreferably comprises steel.

According to a further preferred embodiment the perforations of themiddle section are lined with piping of a material of a high resistanceto chemical attack by the treatment gas.

According to another preferred embodiment of the invention the rearsection comprises a central core and an outer or peripheral partsurrounding the core and the foremost end of which extends past thecore.

The helical duct of the rear section is preferably formed by a helicalgroove in the walls of the core. The helical duct of the rear section ispreferably adapted to communicate with the perforations of the middlesection through a cavity in the foremost part of the rear section.

According to a further preferred embodiment of the invention the rear(lower) part of the middle section and the foremost (upper) part of therear section are provided with threads for screwing the two sectionstogether.

During gas injection into metal melts, particularly melts of relativelyhigh temperature, such as steel melts and ferro alloy melts, throughinjection devices which are inserted in the wall or bottom lining of themelt container, the injection device and particularly the part thereofwhich during operation is in contact with the melt will be exposed togreat stresses. The most highly exposed parts thus have a limited lifeof operation. Interruption of operations for replacing one or more partsof the device should of course be minimised. The device of the inventionhas in operation proved to be particularly reliable and has led to astrongly reduced need for repair and replacement work, and the device isthus considered to represent a technical advance of the art.

The invention will be more readily understood through a description ofexamples of embodiments of the invention, and in the following preferredembodiments of the device of the invention are described referring tothe drawings, examples of embodiments being shown which, especially withrespect to the choice of materials, are adapted to the treatment ofmolen ferro silicon with oxygen-containing gas. It should be understoodthat the gas is passed from a gas source (e.g. a pressure container)through a control panel with the required valves and monitoringinstruments, through the inlet piping of the device and further throughthe injection device and into the melt to be tested.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate, partly in section, the injection device of theinvention in two alternative embodiments. In FIG. 1 the device is shownmounted in the bottom lining of a melt container, whereas in FIG. 2 thelining is not shown.

FIG. 3 illustrates, partly in section, the device of the inventionmounted in the bottom lining of the melt container and an arrangement todemonstrate a suitable way of mounting the device. Certain details ofthe upper part of the device are a combination of the embodiments shownin FIGS. 1 and 2.

In the three drawings the same reference numerals are used forcorresponding parts of the device.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an embodiment of the device of the invention insertedin the bottom lining 9 of a melt container (now shown). The devicecomprises a front section 5 having perforations 10 (of which only twoare shown), a middle section 3,4 having perforations 11, as well as arear section 1,2 having a helical duct 13 running through it. The holes10 of the section 5 correspond with perforations 11 of the middlesection 3,4, the perforations 10 and 11 thus forming passages or ductsbetween the melt and a cavity 12 beneath the middle section 3,4. Thecavity 12 communicates with a source of treatment gas through thehelical duct 13. Thus, a passage for treatment gas is provided from theexternal gas source through the duct 13, the perforations 11 and theperforations 10 to the melt.

As the front section 5 will be contacted by the melt it is made of ahigh melting material, normally a ceramic material, of sufficientresistance to attack by the ferro silicon melt as well as to attack bythe treatment gas. The cross section (or the diameter) of the holes 10(or at least the upper part of each hole) is chosen such that the meltcan not readily penetrate down into the holes even when gas is notinjected through them. A suitable diameter will normally be 2-3 mm.

The middle section 3,4 comprises a part section 4 of copper or copperalloy and a part section 3 made of steel. The reason why copper or acopper alloy, a metal of high thermal conductivity, is chosen is thathigh thermal conductivity results in a quick removal of heat from themelt which (for some reason) might penetrate into the device from themelt container, and the penetrating melt will then solidify in the partsection 4 and block further penetration. Part section 4 of copper orcopper alloy thus comprises a safety measure against the whole devicebeing filled with melt in case melt should break through the frontsection 5 through one or more of the holes 10 (during an intended or notintended cessation of gas injection) or along the interface between thefront section 5 and lining 9 of the melt container, or because of otherdefects that might occur in the front section 5. The thickness of thepart section 4 should be at least 2 cm, desirably more, e.g. 3-4 cm.Optionally, the entire middle section 3,4 may be made of copper orcopper alloy; however this is unnecessary, and the middle section 3,4 istherefore shown comprising two part sections of which the rear partsection 3 is made of steel. The part sections 3,4 may as illustrated bebolted together by bolts indicated by 7. The lowermost portion of thepart section 3 of the middle section has a reduced diameter forconnection to the rear section 1,2.

The rear section 1,2, which suitably may be made of steel, isillustrated comprising two parts, an outer or peripheral part 1 and aninner part or core 2. The rear section 1,2 includes the helical duct 13for supply of treatment gas from the external source to the cavity 12which is defined by the upper surface of the core 2, the lower surfaceof the middle section 3,4 and the upper portion 14 of the outer part 1of the rear section, outer part 14 extending up past the core 2. Forconnection to the middle section 3,4 portion 14 envelopes the lowerportion of the middle section 3,4 and suitably can be screwed onto thelatter.

The device of the invention is, as conventional to such devices,preferably generally conical with circular cross section. The partscomprising the device may be assembled in advance, whereupon thecomplete device may be mounted in the lining 9 of the melt containerafter said lining has been suitably prepared as well known per se.

FIG. 2 illustrates an embodiment of the device of the invention whereinthe front section 5 is divided into two part sections 5a and 5b havingperforations 10a and 10b, respectively, that are communicated through acavity 10c. Although not noly the foremost part 5a, but also the part 5bpreferably is made of a ceramic material, the front section mayadvantageously be diveded into two part sections due to the possibilityof the rear section 5b being intact even if foremost part section 5amust be exchanged after a certain period of operation. Cavity 10centails the advantage that the perforations 10a and 10b in assemblingthe parts 5a and 5b do not necessarily have to be located incorresponding positions straight opposite each other.

The embodiment of FIG. 2 differs from the one of FIG. 1 also by the partsection 3 of the middle section being divided into two parts, 3a and 3b.This may, depending on the circumstances, facilitate the production ofthe part section in question.

FIG. 3 illustrates how the mounting of the device of the invention maybe suitably effected.

The core 2 of the rear section provided with a helical groove on theperipheral surface and forming the duct 13, is welded to the outer part1 of the rear section, core 2 being centrally positioned within theperipheral part 1 with the general surface of the core in contact withthe inner surface of the outer part, whereby duct 13 is formed. A bolt20 is shown screwed in centrally from behind (from the bottom) into abore in the core 2. A bolt 21 supported by a raising/lowering device 22serves to exert an upward directed pressure against the bolt 20 (whenmounting the device of the invention in the bottom lining 9 of the meltcontainer), and also to exercise a downward directed pull on the device(during dismounting), the bolts 20 and 21 being connected by means of aninternally threaded casing 23. The middle section 3,4, the parts ofwhich are held together by means of the bolts 7, are screwed into theupper part 14 of the outer part 1 of the rear section at 24, and thefront section 5 is placed on the top with perforations 10 and 11 incorresponding position. The whole device may then be moved up into theprepared opening in the container lining by executing appropriatepressure.

When dismounting the device the front section 5, sticking due to baking,will normally not come along, but has to be removed in another way,suitably by drilling out. This is a simple and quick operation usingsuitable tools. The melt container must then of course be emptied.

The preferable diameter of the perforations 10 will be somewhatdependent on the hydrostatic pressure of the melt at the outlet of theperforations 10, and on the type and characteristics of the melt, suchas surface tension and viscosity. The exact establishing of the optimaldiameter of perforations 10 is thus a matter of experience in theparticular case of use.

The diameter of the perforations 11 of the middle section 3,4 is lesscritical than in the case of perforations 10, as the middle section isnormally not contacted by the melt. Due to the above mentioned desiredsolidification of melt which, e.g. by accident, might penetrate intoperforations 11 the diameter of the perforations 11 should not be toolarge, and, generally, the diameter suitably may be of the same order ofsize as the perforations 10.

As previously mentioned copper or a copper alloy is the preferredmaterial for the part section 4 of the middle section. Essential ishowever that the part section 4 conducts heat well so that melt whichmight penetrate into the perforations 11 will solidify and preventfurther penetration. Therefore, materials other than copper of coursecan be useful. Alternatively a composite material or a laminate of e.g.steel plates and a mechanically weaker material of better heatconductivity can be employed.

The position of the helical duct 13 through the outer part of rearsection 1,2 has turned out to result in a very favourable cooling effectof the injection gas (temperature gradients). The cooling effect ismainly efficacious in the outer parts of the rear section and in theadjacent parts of the lining 9, but may also to a noticeable degree havea favourable cooling effect inward to the middle section 3,4 andadjacent parts of the lining.

The cross section of the duct 13 of the rear section 1,2 may suitably beof the same order of size as the total cross section of the perforations10 of the front section 5, preferably larger. The total length of theduct 13 will obviously depend on the thickness of the lining 9 in theactual case, as well as the desired distribution of the cooling effectof the injection gas on the different parts of the injection device.Many factors may be of influence here, such as the temperature of themelt, the total thickness of the lining, the heat conductivity of thelining material, the relative length (height) of the three main sectionsof the device, the choice of material for these, among others. Thedevice of the invention can easily be adapted to the particular case ofuse.

The device of the invention is believed to be useful for gas injectioninto any metal melt and similar melts provided that the front section,which is directly exposed to the temperature of the melt and chemicalattack, is made of a suitable material. The choice of material will ofcourse depend on the temperature of the melt and the type of melt,possibly also the nature of the gas at the temperatures to beexperienced, and the selection of material thus will be within the reachof the person skilled in the art in each case.

Referring to the initially mentioned requirements (a)-(f) it will beseen that a high degree of safety that the melt will not flow outthrough the injection device is achieved firstly by suitable choice ofdiameter of the perforations 10 in the front section 5, and secondly inthat melt which might penetrate the front section will solidify in thepart section 4, thereby blocking further melt penetration. The partsection 4 will during injection of gas be cooled by the gas and kept ata relatively low temperature due to the high heat conductivity of thematerial. Efficient dispersion of gas in the melt is achieved due to therelatively low gas flow resistance of the device of the invention andthe fact that the perforations 10 of the front section 5 can readily bearranged in the desired pattern, including perforations having differentdirections and optionally somewhat different diameters.

The requirement of flexibility of capacity mentioned under item c, ismet by the possibility of selection of hole diameter, number of holesand working pressure of the injection gas.

The requirement of long life of the injection device mentioned underitem d, is primarily met by selection of a suitable refractory materialfor the front section, but also by the cooling effect resulting from agas flow through the disclosed device of the invention.

The requirement of possibility of simple and quick replacement from theexterior wall/base of the container mentioned under item e is met by thefact that

the outer surfaces of the injection device can readily be treated withsuitable sealing/release agents during mounting,

the rear and middle sections of the injection device can be retractedfrom their positions in the container lining by screw means inconnection with the device 22 shown in FIG. 3, which during operation ofthe injection assembly also keeps the injection device in position inthe container lining,

when required the front section of the device can quickly be removed bydrilling and a new front section installed.

The requirement of adaptation possibilities mentioned under item f ismet by the feasibility of manufacturing the three main sections of thedevice to have specific, desired length and diameter dimensions.

As is apparent from the above, the device of the invention may,substantially, be made of steel, suitably common carbon steel, which isconsidered to be an advantageous feature

We claim:
 1. Device for injecting gas into a hot melt, particularly molten metal, which device is suitable for being installed in the wall, particularly the bottom wall, of the container holding the melt, wherein said device comprises three main sections including:a front section of refractory material which is resistant to the hot melt and which has a number of perforations for introduction of gas into the melt, a middle section which at least partly consists of heat conductive material and possesses a number of perforations communicating with the perforations of the front section, and a rear section at least an outer part of which is of heat conducting material, which rear section in or close to its peripheral parts has a helical duct communicating with the perforations of the middle section and adapted to pass said gas from an external gas source into the hot melt.
 2. Device according to claim 1, wherein said front section is divided into two part sections of which at least a foremost said part section is made of a refractory material, and the perforations of said foremost part section communicate with the perforations of the other part section through a cavity.
 3. Device according to claim 1, wherein said middle section is divided into two part sections of which at least a foremost said part section is made of a material having high heat conductivity.
 4. Device according to claim 3, wherein said foremost part section of the middle section is made of copper or a copper alloy.
 5. Device according to claim 3, wherein a rear part section of the middle section is made of steel.
 6. Device according to claim 1, wherein the perforations of the middle section are lined by piping of a material of high resistance to chemical attack by the treating gas.
 7. Device according to claim 1, wherein said rear section comprises a central core and an outer or peripheral part surrounding the core and having a foremost end which extends beyond the core.
 8. Device according to claim 7, wherein said helical duct is formed by a helical groove in the side walls of the core.
 9. Device according to claim 1, wherein the helical duct of the rear section communicates with the perforations of the middle section through a cavity in the foremost end of the rear section.
 10. Device according to claim 1, wherein the rear (lower) part of the middle section and the foremost (upper) part of the rear section are provided with threads for screwing together said two sections. 